Pressure is mounting on Brian Cowen to step down as Ireland's prime minister after one of the governing coalition's partners called for a general election and backbenchers in his own Fianna Fáil party moved against him.

Meanwhile, the Green party today said the electorate felt "misled and betrayed" by recent events and they now needed "political certainty".

The moves by the Greens and the pressure from within Fianna Fáil increase the likelihood of a general election in the new year.

The Greens pledged to support Cowen's administration until the negotiations with the International Monetary Fund and the European Union are concluded, but said it wanted the country to go the polls in the second half of January.

"Leaving the country without a government while these matters are unresolved would be very damaging and would breach our duty of care," the party said in a statement. "But we have now reached a point where the Irish people need political certainty to take them beyond the coming two months."

John Gormley, leader of the Greens, said he had discussed the issue with Cowen, who had expressed disappointment about their decision.

Gormley said the party had always said it would only continue in the administration as long as it would benefit the people, but leaving the country without a government would be damaging and breach is duty of care.

He said the decision was made last Saturday after a long series of meetings. At a specially convened press conference in Dublin today, he said the last three weeks had been traumatic for Irish people.

"Since entering government in June 2007, we in the Green party have worked to fix and reform the economy. It has been difficult. We have taken tough decisions and put the national interest first," he said.

Gormley said there had been significant communication problems within government in recent days, and that the Greens had not been able to receive clear answers to their questions.

Pressure on Cowen to resign had mounted today with two backbenchers breaking ranks. Cork TD Noel O'Flynn called on Cowen to step down after the budget.

Fianna Fail veteran Mary O'Rourke, a former minister, fanned the flames of dissent further by calling for a party summit in January to discuss the questions of the leadership and an election.

"I would support the Taoiseach until the budget and the finality of that, after that I think the Fianna Fail should meet in the first week in January and as a party we should decide on our future together," she said.

O'Rourke is part of one of Ireland's oldest political dynasties – her nephew Brian Lenihan is the finance minister and her late brother Brian Lenihan Snr was one of the most prominent politicians in Ireland in the 80s and 90s.

Party sources have told the Guardian that support for Cowen is slipping after he repeatedly denied that Ireland needed a bailout.

"We cannot go into a general election with Brian as leader after the events of last week. His credibility is shattered," one senior Fianna Fáil source said.

As eurosceptic Conservatives prepared to raise their concerns with the chancellor in the Commons this afternoon, Osborne said that Britain was simply preparing to help its closest neighbour in its hour of need.

"Ireland is a friend in need and we are here to help," the chancellor told BBC Radio 4's Today programme ahead of a Commons statement this afternoon.

However, the prospect of Britain supporting the Irish rescue package has alarmed some eurosceptic politicians.

"We shouldn't be paying to help keep Ireland in the euro. If we are going to pay to solve this crisis we should be helping to pay Ireland to quit the euro," the Conservative MP for Clacton, Douglas Carswell, told the BBC.

There are fears across Europe that a multibillion euro bailout will not be enough to contain the latest economic crisis. Our expert panel discusses how Ireland got into this precarious position – and which countries could be next